The present invention relates to a method of operating a GPS receiver for the acquisition of GPS signals through the processing of a received signal over an integration time period and including the step of switching the integration time period of the receiver between two discrete values.
GPS devices are arranged to provide accurate positional information and are employed increasingly with mobile communication devices so as to allow for a relatively accurate determination of the geographical location of the communications device at any particular time. GPS receiver devices are arranged for the acquisition of GPS signals transmitted from a constellation of satellites and, generally through the employment of three separate GPS signals, calculate the receiver""s location based upon a predetermined acquisition strategy. Such strategy can include a determination of which one or more satellites to search for, the particular integration time within which each satellite signal is processed and the identification of an acceptable time period within which to expect to acquire the required signal. One such factor, i.e the integration time period required for processing the received signal will differ depending upon the strength of the incoming signal. For example, in strong signal conditions, integration times in the region of 1 ms for each satellite can prove acceptable for detection and signal acquisition whereas, in environments where the GPS signal maybe somewhat attenuated, for example in forests, and built-up areas and generally enclosed areas, longer integration times will be required in order to achieve the necessary processing gain to compensate for such attenuation. Current GPS receivers are arranged to process the received GPS signals over an integration period of between 1 and 10 ms.
While, in practice, most GPS receivers at present only offer suitable functionality to integrate for 1 ms, it has been proposed that a receiver control arrangement be provided such that, if insufficient satellite signals are detected after a predetermined period, for example, 10 seconds, then the integration time is increased to, for example, 10 ms.
U.S. Pat. No. 6,133,873 discloses such a method for adaptively processing a GPS signal in an attempt to optimize the initial acquisition of GPS signals wherein, if a GPS signal is not appropriately received within a predetermined integration time, the integration time is increased before another attempt is made to receive the signal.
Also, it has been proposed that a predetermined maximum time limit be provided for acquisition such that, if no satellites are detected within that predetermined period, the user is then prompted to indicate whether the GPS receiver might be positioned in a location, for example indoors, where receipt of the GPS signals is unlikely to be achievable such that no further battery power need be wasted in attempting signal acquisition.
In general, the calculation of location in GPS systems changes in different environments and a move to a new environment causes a delay in the system while the new location is calculated using the standard integration time. In this manner, integration time is not optimised and this can lead to disadvantageous delays in signal acquisition and wastage of battery power.
Although it could be considered that the prior-art problems could be overcome merely by increasing the integration time so as to allow for operation of the GPS receiver when experiencing poor signal-acquisition conditions, such a strategy can prove disadvantageous in that, for each increase in integration time, the acquisition time increases at an exponential rate. Thus, if the integration time is increased by a factor of 10, the acquisition time is likely to increase by a factor of 100, as does the power consumption of the receiver circuitry.
As suggested above, location calculation within a GPS system is relatively power consuming and also represents a complex calculation which, even in good signal conditions, will take in the region of 1-15 seconds. Thus, excessive power consumption is particularly undesirable in mobile devices employing on-board power sources. A long acquisition time is also an undesirable aspect since a user will in any case wish to obtain a position-fix as quickly as possible.
The present invention seeks to provide for a GPS receiver arrangement and related method of offering advantages over known such receivers and methods.
According to one aspect of the present invention, there is provided a method of operating a GPS receiver as defined above, and characterized by the steps of switching between the said two discrete values of integration time period in response to a signal indicative of the environment in which the receiver is located.
The present invention is advantageous in reducing acquisition time by optimizing integration time on the basis of local environmental factors and so as to decrease the prevailing average power consumption and thus acquisition time. In seeking to optimize the integration time period for processing the received signal, power wastage and delays can therefore be reduced in poor signal conditions since the receiver does not first attempt a position fix within appropriately short integration times, and in strong signal conditions by not employing unnecessarily long integration times.
As further described below, certain aspects of the invention prove particularly advantageous in improving the flexibility of response offered by the invention to different environmental conditions. Moreover, to allow for a particularly accurate, but readily altered, selection of appropriate integration time periods and allow for alternated, and accurate, control of the integration time period. Still further, the certain aspects of the invention enable a successful acquisition strategy can subsequently be employed so as to reduce future power overheads when signal acquisition is required under similar environmental conditions and in improving the flexibility and simplicity with which environmental conditions can be recognized.
According to another aspect of the present invention as provided a GPS receiver arranged for the acquisition of GPS signals through the processing of the received signals over an integration time period, the receiver being arranged to operate with either of at least two discrete integration time periods and including control means for switching between the said integration time periods, characterized in that the said control means is responsive to a signal indicative of the environment within which the receiver is located.
Advantageously, the invention can provide for such a receiver and including means arranged for operating in accordance with any one or more of the method steps defined above.